1. Field of the Invention
The present invention relates to an improvement in the technology of beam-welding aluminum-plated steel panels into an assembly such as a fuel tank for use on motor vehicles.
2. Description of the Related Art
Fuel tanks for use on motor vehicles such as motor scooters or the like are generally made of tin-lead-plated steel panels or zinc-nickel-plated steel panels for making their inner surfaces resistant to corrosion. Since certain legal restrictions are imposed on the use of plated lead layers for environmental protection purposes, however, there have been demands in the art for fuel tanks of other materials. One such fuel tank is made of steel panels each having fusible plated aluminum layers on its both surfaces, the steel panels having marginal edges superposed one on the other and welded to each other. Because of the plated aluminum layers on the both surfaces of the steel panels, the fuel tank of this structure is corrosion-resistant on its inner and outer surfaces.
Generally, steel panels for making up fuel tanks have heretofore been welded by resistance seam welding. If the resistance seam welding process is employed to weld steel panels each having fusible plated aluminum layers on its both surfaces, then it suffers the following drawbacks:
The welding electrodes of the welding machine need to be cleaned and shaped frequently because plated aluminum segments tend to be attached to the welding electrodes during the welding process.
Since the plated aluminum layers are highly conductive of heat and electricity, the steel panels cannot be welded unless they are supplied with a large electric current which is 1.5-2.0 times the electric current which is required by ordinary steel panels.
Because the amount of heat applied to the steel panels is large during the welding process and hence the surface layers of the steel panels are destroyed in a wide area by the applied heat, a surface treatment subsequent to the welding process is required especially on the inner surface of the fuel tank to withstand corrosion.